1. Field of the Invention
The present invention relates to a method and apparatus for recovering gases. The areas of application are the anesthetic gases used in human and veterinary medicine as well as the recovery of gases from expired air. The apparatus allows the intermediate storage of gases in appropriate zeolites and the complete recovery of the gases from the gas mixtures produced during the application by way of a thermally induced expulsion from these zeolites.
2. Discussion of the Background
There are known apparatuses with whose help gas mixtures, during their introduction into defined chemical substances, are split up in such a way that the desired separation is carried out mostly by a chemical reaction. In this way, new compounds arise which are either disposed of in their present form or are stored over a long period of time however, in most cases these compounds are very difficult to recover. Examples of adsorptive gas cleaners based on the principal of flow through a suitable chemically active liquid are the so-called scrubbers as are found in the semiconductor industry in applications with highly toxic process gases, or also different types of dry bed absorbers whose active components can be optimized for the different kinds of gases to be separated. All these arrangements show the same disadvantage in that they are not equipped for economically recovering the gases adsorbed in these devices. It is equally commonly know that besides the known absorption which takes place in suitable liquids and solid materials, micro-porous solid-state bodies such as zeolites, active carbon among others, can adsorb certain materials while heat energy is given off and can desorb certain materials while heat energy is being received. Similar process take place during the physical state changes of matter (e.g., ice-water-vapor).
The prior art presents a number of publications for sorption of the different kinds of gases in liquids, solid absorbers but also zeolites and other micro-porous solid-state bodies. Filters for gas masks likewise absorb and adsorb completely the harmful substances until a saturation limit is reached. Beyond this limit it is relatively easily controllable that the substances will go through practically uninfluenced. This means that a limit point is always set-up for the adsorbed gases e.g. anesthetic gases in which the sorbents and the sorptives are equally balanced. This point is substantially dependent upon the pressure and temperature of the components.
The technical, physical and chemical prerequisites for the highest possible sorption capacity together with an optimal regeneration ability of the sorption equipment are described in the patent documents DE 3731688, DE 3628858 and DD 239947. Documents DE 4003668 and DE 3713346 report on the removal of halogenated carbon hydroxides by means of zeolites. Described in the published document DE 19549271 is a method in which silicium rich zeolites are employed for recovering gases with different vapor pressures from gas mixtures. In this document no information is given about the Si/Al ratio. Zeolites are suitable as well for removing substances from watery solutions (DE 44 06776 and DE 19531933). Recently, in particular reduced aluminium and dealuminated zeolites have found use as an adsorption means as can be taken from patent document DE 19532500; Document DE 4233577 describes the sorption of halogenated carbon hydroxides onto dealuminated zeolites.
The known commercially used arrangements show the common feature that either the substances isolated by the sorption process stay put and are disposed together with the sorbents, for example in appropriate combustion plants, or also taking the chemical path are changed into relatively harmless products and are then deposited. In this way, among others certain gas masks are filled with sorbents consisting mostly of modified active carbon.
U.S. Pat. 3,592,191 reports on the recovery of anesthetic gases with absorbing material. At the same time the water vapour is bound by means of a hydroscopic material.
Otten, Gail and Frey (Chem.-Ing.-Tech. 64 (1992) No. 10, 915-25) present a dealuminated Y-zeolite having a SiO2/Al2O3 ratio of over 200 suitable for cleaning expired air and recovering solvents e.g. from toluene. These high dealuminated zeolites show however still a good adsorption ability for polar substances. Patent EP 0284227 describes an apparatus and method in which alumosilicates can absorb up to 15 percent-by-weight of anesthetic gases having relatively small molecule diameters. In the method presented there a recovery is also suggested in such a way that a carrier gas which has been heated up flows through the filled adsorber, brings a greater part of the adsorbed gases to be desorbed and by a subsequent cooling down to low temperatures which are gained from vaporizing liquid nitrogen, can condense again in a suitable container and thereby be led to reuse. Employed are zeolites having a SiO2/Al2O3 ratio greater than 50. The recovery rate in this method lies considerably under 50%; no statement is made on the quality of the recovered gases. In this method sevolfluran is not separated. Since the alumosilicates used in this patent however comprise of a relatively high share of aluminium which is known for its catalytic activity with the anesthetic gases being considered which are all halogenated carbon hydrides, a direct reuse does not appear possible in view of the expected catalytic resultant products. The necessarily high temperature for desorption by means of hot carrier gases increase this effect even more.
The almost complete recovery of anesthetic gases has not yet been described.
The object of the invention is to provide a method and apparatus for the sorption of principally gaseous substances, for example, anesthetic gases, and which allow to make it possible to almost completely recover these substances, for example, to recover the substances in air expired from the patient for the purpose of saving costs or to relieve the environment while requiring the least possible amount of energy and having the least affect on the composition of the anesthetic gases.
This object is satisfied in that by making use of desorption processes adapted in a suitable way, individual components of the mixture are bound above a temperature specific to the substance in adsorbing zeolites while other components pass these zeolites wherein the adsorbed gas is desorbed by way of heating up the adsorbing substances, is liquified in a following condenser and is fed for reuse.